This invention relates to connections between a metallic component of an assembly and a non-oxidic ceramic (ceranox) component of an assembly capable of withstanding high thermal and mechanical stresses. The present invention also relates to methods for producing such connections.
In certain applications it is desirable to replace conventional metallic components with ceramic materials. This is particularly true in gas turbine engines where the use of ceramic materials for certain components, such as turbine blades or turbine rotors, enables an increase in the efficiency and performance of the engine by an increase in the operating temperature which can be maintained in the vicinity of the turbine blades and turbine rotors as compared to gas turbine engines having such components made from conventional metallic materials, which exhibit limited operating temperature ranges, owing to the relatively low thermal resistance of metal. Ceramic materials preferably considered for turbine rotors and blades include Ceranox ceramics, that is non-oxidic ceramic materials, such as silicon carbide and silicon nitride.
The use of such ceramic materials is often inhibited by difficulties which are encountered in forming a connection between components made with non-oxidic ceramic materials and components which are made from conventional metallic materials, for example when attaching a ceramic turbine rotor to a metallic turbine shaft, or mounting ceramic turbine blades in a metallic turbine rotor. Such difficulties arise in part because of the relatively high brittleness of the ceramic materials, which exhibit practically no plastic deformation or flow when subjected to stress. Hence, unlike metallic materials, such ceramic materials are incapable of reducing the local stress peaks occurring in the course of operation. Stress peaks may be caused by unavoidable manufacturing tolerances or by the uneven thermal expansion of the metallic and ceramic components. For this reason no edge or even point contact is permissible between ceramic and metallic components, so that the components to be connected by prior art techniques required expensive precision manufacturing and processing methods, with a high surface quality and accuracy.
It is therefore an object of the present invention to provide an assembly having a new and more reliable connection between components consisting of ceranox and components made from metallic material.
It is a further object of the present invention to provide such an assembly which can endure high thermal and mechanical loads.
It is a further object of the invention to provide an improved turbine assembly having ceramic turbine blades mounted to a metallic turbine rotor.
It is a further object of the invention to provide an improved turbine assembly comprising a ceramic turbine rotor mounted on a metallic turbine shaft.